Translatory precision potentiometer



y 1962' J, w. ALEXANDER ET AL 3,036,284

TRANSLATORY PRECISION POTENTIOMETER Filed May 20, 1960 2 Sheets-Sheet 1 I26- 2 I I24 9 /0 INVENTORS ATTORNEY May 22, 1962 J. w. ALEXANDER ET'AL 3,036,234

' TRANSLATORY PRECISION POTENTIOMETER Filed May 20, 1960 2 Sheets-Sheet 2 Z4 9 ./0//4/ M41. M44 445(AA/06 ATTORNEY United States Patent TRANSLATORY PRECISION POTENTIOMETER John W. Alexander and William A. M. Trnesdell, Binghamton, N.Y., assignors to General Precision, Inc., Binghamton, N.Y., a corporation of Delaware Filed May 20, 1960, Ser. No. 30,528 5 Claims. (Cl. 338-183) This invention relates to an improved translatory precision potentiometer in which the contact pressure of the sliding contact on the resistance element is extremely uni-form throughout the range of travel of the sliding contact. In particular, this invention relates to an improved translatory potentiometer in which the resistance element and the contact carrying carriage member are held a fixed distance apart, within extremely close tolerances, throughout the entire travel of the carriage memiber (i.e., throughout the entire range of travel of the sliding contact).

In many branches of the electronic arts, and more particularly in the analog computer, servomechanism, and automatic control and instrumentation arts, translatory precision potentiometers are extensively used. Such potentiometers are used, for instance, where the desired input data for an analog computer must be converted from a mechanical displacement to an electrical voltage with a high degree of precision. It is necessary in order to achieve this high degree of precision that the sliding contact on the potentiometer bear upon the resistance element with the same pressure throughout the entire range of travel of the sliding contact. It is well known that many prior art translatory precision potentiometers have not achieved this necessary uniformity of contact pressure to the degree desirable in many applications in the analog computer, servomechanism, and automatic control arts.

The present invention overcomes the contact pressure variation problem, and associated problems, by providing a rail member rigidly mounted at a fixed and uniform distance from a base member upon which the resistance element is disposed, and by further providing a carriage member carrying the sliding contact, which carriage member rides upon the rail member in close fit relation thereto. Since the rail member upon which the carriage member rides is uniformly spaced from the base member, the carriage member is also necessarily uniformly spaced from the base member throughout its range of travel and, thus, the sliding contact bears upon the resistance element with uniform pressure throughout its operating range.

\ This uniform pressure assures a high degree of correspondence between the input mechanical displacement and the output voltage (or resistance) which is highly desirable in many applications.

One of the objects of the invention resides in the pro vision of a translator-y precision potentiometer wherein the linearity established between the input mechanical displacement and the electrical output is better than has heretofore been possible by any means established under the prior art.

I Another object is to provide an improved translatory precision potentiometer wherein the contact pressure between the sliding contact and the resistance element is uniform throughout the range of the travel of the sliding contact. a

A still further object of the invent-ion is to provide an improved translatory precision-potentiometer wherein the distance between the member bearing the sliding contact and the resistance element is uniform throughout the range of translation of the sliding contact.-

f Yet another object of the invention is to provide an improved translatory precision potentiometer wherein misalignments of the drive means cannot produce substantial variations in the pressure of the; sliding "contacts upon the resistance element; thus reducing the excessive wear, shortened potentiometer life, and undesirable variations in electrical characteristics which characterize the translatory precision potentiometers of the prior art.

' Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the features of construction, combinations of elements, and arrangements of parts, which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention reference should be had to the following detailed description taken in connection with the accompanying drawings in which:

FIG. 1 shows a section only of the translatory precision potentiometer of the invention.

FIG. 2 is a detailed side View in section (plane 22) of the structure shown in FIG. 1.

FIG. 3 is a detailed side view in section of an alternative embodiment of the invention.

- FIG. 4 is a perspective cut-away view of the potentiometer of the invention, including a protective casing which may be employed as desired.

FIG. 5 represents schematically a circuit utilizing the invention.

' Referring to FIGS. 1 and 2, the potentiometer of the invention includes a frame member 10 composed of nonconducting material, upon which are supported resistance element 2, pickup track 9, and guide track, or channel, 13. Resistance element 2 comprises an insulatingly coated metal mandrel 14 upon which is wound a resistance wire coil 16. The insulating coating is shown at 15.

Alternative constructions of resistance element 2 will, of course, readily occur to those skilled in the potentiometer art. For instance, instead of employing a woundmandrel construction the resistance element may comprise a single rod of a properly selected high resistance material. Additionally, resistance element 2 may comprise an insulated metal mandrel upon which a resistive coating, rather than a resistance coil, is disposed. In some cases it maybe desirable to employ as resistance element 2 a non-conductive, insulating mandrel upon which a resistance winding, or a resistive coating, is deposited. Also, resistance element 2 may comprise separate, colinear sections, each section being equipped with its own terminals. Alternatively, resistance element 2 may be shaped, rather than linear, i.e., the resistance measured from one end of the resistance element to the contact may vary non-linearly with carriage movement in'a predetermined manner. It may also be desirable to introduce discontinuities in resistance element 2 by conductively short circuiting selected portions thereof.

Pickup track 9 comprises a highly conductive metal stratum, or coating, fastened directly to frame member 10, or coated directly thereupon; Pickup track 9 may, in some cases, comprise separate colinearsections, each section being equipped with its own terminals. -Frame 10 is fastened to a series of C-brackets 1., 1 by means of machine screws 19. C-brackets 1,1 are in turn secured to guide rail 6 by means of machine screws 18. 'By means of the C-brackets 1, 1 and collars 22, guide rail 6 is main- .tained at a fixed and uniform distance from frame 10. Carriage 5 rides upon rail 6 in slidable and close fitting relation therewith. A plurality of contacts 12a, 12b are mounted on carriage 5 by means of spring leaves 3. Either, or both, carriage 5 or rail 6 may be suitably fabricated from conductingmaterials. When carriage 5 is comprised from conducting material it may be desirable to insulate the leaf spring-contact assembly 3, 12a, 12b from carriage 5 by meansegz, of insulating shim 8'. As shown in FIGURE 2, the two contacts 12 are connected 3 in series relation through spring leaves 3. That is to say, spring leaves 3 may be fabricated from a single piece of material (e.g., beryllium-copper) such that a continuous circuit is provided between the contacts 12 by a conductive path through spring leaves 3 and their common bridge member. Alternatively, spring leaves 3 may be separately fabricated and then joined by conductive bridge means. Also mounted upon carriage is alignment pin 4. Alignment pin 4 rides in the guide track 13 of frame member in order to insure fixed angular displacement of carriage 5 as it traverses along rail 6. Drive pin 7, or its equivalent, is provided in order that motion, corresponding to a given input mechanical displacement, may be imparted to carriage 5. Suitable means for imparting such motion is schematically illustrated at 21 in FIG. 4. Drive pin 7 may be actuated in many other manners which will occur to those skilled in the art. For instance, drive pin 7 may be attached variously, to a chain, wire, or metal belt drive. Carriage 5 may, of course, be driven by many other suit-able means'from drive pin 7. Such means will readily occur to those having ordinary skill in the art. For the conversion of some types of rotary motion with a high degree of precision it may also be desirable to attach drive pin 7 to a follower in the groove of a face plate cam. It will be noted that the provision of alignment pin 4, having a close, sliding fit in guide track 13, affords a means ,of maintaining carriage 5 against rotation around the axis of rail 6. Thus, the pressure of contacts 12a and 12b upon track 9 and resistance element 2, respectively, is maintained individually, one completely independent of the other. By this means, it is assured that the pressure of contact 12b upon resistance element 2 will remain uniform throughout the range of travel of carriage 5 whether leaf springs 3 and contacts 12a and 12b are of the same or dilferent material, or are stressed to the same or difierent degrees.

Numerous variations of the construction shown in FIGS. 1 and 2 may be employed within the spirit and scope of the invention. For instance, as shown in FIG.

3, to insure better alignment under heavy loads a plurality of rails 6 may be employed and alignment pin 4 eliminated. Also, where heavy loads are involved, or high acceleration inputs, a ball bushing may be employed between carriage 5 and rail 6, rather than the sliding bearing illustrated herein. In addition, as shown in FIG. 3, it may be found desirable in particular applications to employ a plurality of pick-up tracks '9, or a plurality of resistance elements 2, or a combination thereof.

Shown in FIG. 4 is a casing or dust cover which may be employed in any application where it is found desirable. Also shown in FIG. 4 is an actuating means 21 for drive pin 7. Actuating means 21 is shown only schematically and may, in a given application, consist of a rigid metal drive rod, a chain, a wire, or metal band drive, a linear electric motor, worm and nut means, pneumatic, or hydraulic means, or other expedients suggested hereinabove. Actuatingmeans 21 may, of course, bev secured directly to an end portion of carriage l5, rather than to a drive pin attached thereto.

Rail 6 may, of course, have a shape other than the circular cross-sectional shape indicatedherein. Rail 6 may, for instance, be rectangular in cross-section, thereby obviating the need'for. alignment pin 4. It may be desirable in some applications to provide plural carriages on separate rails which maybe separately driven, or mutually adjustable as torel'ative linear displacement. According to one embodiment of the invention, the potentiometer may comprise two or more resistanceelements, nad no pickup tracks.

It will be evident from inspection of FIG. deflection of carriage 5 will be accurately shown by :a

proportional deflection of galvanometer24. The signal 5 7 that 7 each} It will be desirable in some applications to provide adjustment means whereby the resistance element, or elements, pickup track, or tracks, and the contacts may be fixed in any desired relative linear displacement.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained. Since certain changes may be made in carrying out the above process, in the described product and in the constructions set forth without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of. the invention which, as a matter of language, might be said to fall therebetween.

Having described my invention, What I claim as new and desire to secure by Letters Patent is:

1. A translatory precision potentiometer comprising: an insulating frame member formed of a plurality of spaced apart C-shaped members, said frame member carrying a resistance element and a conductive pickup track; a rail member rigidly mounted at a uniform distance from the plane of and parallel with said resistance element and said pickup track; a carriage mounted upon said rail member and bearing a plurality of contacts which bear upon and electrically contact said resistance element and said pickup track respectively, said contacts being series connected; and drive means connected to said carriage whereby said carriage may be displaced in proportion to a given mechanical input signal,

2. A translatory precision potentiometer comprising: an elongated frame member comprising a plurality of spaced apart C-shaped members; a rail member parallel to said frame member; said frame member carryinga longitudinally-disposed resistance element and a conductive pickup track; said rail member carrying a slidable carriage; a pair. of series-connected resiliently-mounted, contacts carried upon said carriage and bearing conductively upon said resistance element and said pickup'track respectively; input drive means for said carriage member whereby input mechanical displacements may be imsaid pickup track and said resistance element extending longitudinally of said insulating frame member; a slidable carriagemounted upon said rail member; a plurality of series-connected, flexibly-mounted contactsrmounted upon said carriage and in slidable, conductive contact with said resistance element and said pickup track; mechanical drive means for'said carriage whereby an input mechanical displacement maybe applied thereto; and terminals connected to said pickup track and to both ends of said resistance elementrwhereby electrical excitation may be 7 applied to said resistance element and an'output voltage 1 signal may be derived from said pickup track.

4. A translatory precision potentiometer comprising: resistance means; rail means mounted parallel thereto on an insulating frame member comprisinga plurality of C-shaped members; carriage means slidably mounted 7 upon} said rail means; contact means resiliently mounted tacting'said resistance means; and terminal means whereby upon said carriage means and slidably, conductively conelect rical excitation'may besupplied to said resistance means and an electrical output signal may be derived from said contact means.

5. A translatory precision potentiometer comprising: rail means; frame means mounted parallel thereto and at a fixed distance therefrom; said frame means comprising a plurality of spaced apart O-shaped frame members collectively carrying at least one conductive pickup means and at least one resistance means, said pickup means and said resistance means extending longitudinally of said frame means; slidable carriage means mounted upon said rail means; a plurality of resiliently mounted contact means mounted upon said carriage means and in slidable, conductive contact with said resistance means and said pickup means; mechanical drive means for said carriage means whereby an input mechanical displacement may be applied thereto; and terminal means connected to said pickup means and to both ends of said resistance means whereby electrical excitation may be applied to said resistance means and an output voltage signal may be derived from said pickup means.

References Cited in the file of this patent UNITED STATES PATENTS 2,706,230 Bourns et al Apr. 12, 1955 2,785,262 Bourns Mar. 12, 1957 2,805,307 Bourns et al. Sept. 3, 1957 2,945,199 Mucher et al. July 12, 1960 

